Field of the Invention
The present invention relates to an ultrasonic motor for driving a member to be driven by generating an ellipsoidal vibration on an impressed vibrator, and to a lens apparatus using the ultrasonic motor.
Description of the Related Art
An ultrasonic motor has been conventionally used as a driving source for driving, for example, a lens mechanism or a camera, taking advantage of silent operation, driving capability from low speed to high speed, and high torque output. For example, an ultrasonic motor disclosed in Japanese Patent Application Laid-Open No. 2006-158052 includes an annular member to be driven having a rotation axis, and multiple vibrators each including a contact part coming into contact with the annular member to be driven. The vibrator is retained in a state of being impressed against the member to be driven, rendering the contact part of the vibrator and the member to be driven in a so-called pressurized contact condition in which the contact part of the vibrator is pressurized against the member to be driven to bring them into contact with each other. When an ultrasonic vibration is excited on the vibrator under the pressurized contact condition, an ellipsoidal motion is generated on the contact part of the vibrator, so that the member to be driven is driven to rotate about the rotation axis of the member to be driven. The pressurized contact condition of the vibrator with respect to the member to be driven is obtained by biasing the vibrator against the member to be driven with use of a plate spring having a convex part for impressing the vibrator. The contact part of the vibrator comes into pressurized contact with the member to be driven in an appropriate state by impressing and biasing the vicinity of the center of the vibrator with a plate spring having the convex part for impressing the vibrator.
However, in the ultrasonic motor disclosed in Japanese Patent Application Laid-Open No. 2006-158052, there is a problem that the contact part of the vibrator and the member to be driven cannot come into pressurized contact in an appropriate state due to a manufacturing error or deformation of the plate spring.
In addition, in the ultrasonic motor disclosed in Japanese Patent Application Laid-Open No. 2006-158052, the convex part for impressing the vibrator is formed on the plate spring, and hence the convex part for impressing the vibrator and the contact part of the vibrator are likely to be shifted with respect to each other without keeping a consistent positional relationship therebetween due to an error between members, an assembling error, a manufacturing error, or deformation of the plate spring at the time of pressurization. Therefore, there is a problem that a direction of impression by the plate spring is deviated, so that a consistent contact condition cannot be maintained between the contact part of the vibrator and the member to be driven, and in some cases, a contact failure occurs.
Further, the contact parts of the vibrators are arranged in a driving direction of the member to be driven, and hence each vibrator is likely to be inclined in a direction perpendicular to the driving direction and parallel to the contact part of the vibrator rather than in the driving direction. The inclination of the vibrator may cause a problem that a partial contact occurs on the contact part, so that the contact part of the vibrator and the member to be driven cannot come into pressurized contact in an appropriate state.